This disclosure relates to reinforced polymeric materials, methods of manufacture thereof and articles comprising the same.
The mechanical and rheological properties of organic polymers can be altered by the addition of a second phase that can be miscible or immiscible with the organic polymer. Increasing the impact toughness of organic polymers has generally been accomplished by several different methods.
One method of improving the toughness comprises producing a composite by incorporating a second phase into the organic polymer matrix so as to increase the tortuousity of the crack trajectory. The second phase generally is softer than the organic polymer. Another method is to develop crack wake mechanisms like crack bridging and crack pinning. Yet another method involves developing crack front mechanisms that absorb energy and delocalize the stresses at the crack tip.
As noted above, one universal method for improving the impact strength and fracture toughness of organic polymers has been to produce a composite by dispersing soft organic polymeric particles having a particle sizes of about 0.1 micrometers to about 10 micrometers into a higher-modulus organic polymer matrix. The soft organic polymeric particles are commonly added in concentrations of about 5 to about 20 volume percent, based upon the properties of the soft particles, the organic polymer matrix, and the interface properties.
When the local stresses in front of the propagating crack tip becomes excessive, the soft particles either cavitate or disbond from the organic polymer matrix prior to fracture. The cavitation or disbonding, in turn, locally relieves hydrostatic stresses in the composite and allows for yielding and inelastic flow to occur in the organic polymer matrix. Both the cavitation process and the subsequent flow of the organic polymer matrix facilitate energy dissipation with the majority of energy dissipation occurring due to the matrix flow. This macroscopically alters the failure mode from a brittle to a ductile process that consumes energy and avoids a catastrophic fragmentation of the organic polymer matrix. This method is generally used to toughen organic polymers for applications ranging from sports equipment to automotive and aerospace applications. The drawback to this strategy is that the modulus of the organic polymer is decreased by the introduction of the soft particles. In addition, the process viscosity undergoes a change due to the addition of the soft particles. This change in process viscosity limits the ability to put in other reinforcements or additives. In order to offset these drawbacks, systems are often optimized to develop the best balance of properties for specific applications. There are no organic polymer compositions that combine a low melt viscosity with improved toughness and an increased elastic modulus.
It is therefore desirable to have a polymeric composite that can display a low melt viscosity, high impact strength, and a high elastic modulus.